1. Field
The invention is in the field of mechanical latches, especially power-operated mechanical latches of the pivoted latch element type currently in use for latching and unlatching the cab of an automotive truck that has its cab pivoted to be swung open and closed relative to the engine of the truck, see for example Brimhall U.S. Pat. No. 3,797,882 and Nordell et al. U.S. Pat. No. 3,752,519.
2. State of the Art
In the aforementioned Brimhall patent, latching of a hooked latch element over a keeper bar is effected by the action of a small spring to move such latch element laterally toward the keeper bar following longitudinal retractive movement thereof, while in the aforementioned Nordell et al. patent similar lateral latching movement is effected by camming action on the back of the hooked latch element during such longitudinal retractive movement. In both instances, the longitudinal retractive movement of the hooked latch element is effected by the action of a relatively large and powerful, compressive, coil spring. In both, longitudinal extension of the hooked latch element (so that lateral movement thereof away from the keeper bar at the end of the extension stroke results in unlatching), is effected by the piston of a hydraulic power cylinder. At such time as hydraulic pressure on the piston is released following unlatching by reason of the power stroke of the piston, the powerful spring retracts the hooked latch element to its original retracted position. The hydraulic systems contemplated by these patents maintain pressure on the piston during all times that the hydraulic pumps incorporated in the respective systems are operating, so the latching element is effectively maintained in its extended position.
There are hydraulic systems, however, in this field of use that maintain pressure only during alternate strokes of the pistons of positive displacement pumps component to such systems, leaving no supportive pressure for the piston of a hydraulically actuated cab latch if incorporated into such a system. As a consequence, retraction of the hooked latch element following each power stroke of the pump piston would tend to relatch the cab before the cab lift cylinders could lift the cab sufficiently to prevent such relatching. Accordingly, the patented cab latches have not been employed with hydraulic systems of this type.
3. Objectives
It was a primary objective of the present invention to so construct the cab latches of the specified patents as to be useful in these other hydraulic systems, and to do so with a minimum of structural and functional changes in the original design.